Method of making primary current detector using plasma enhanced chemical vapor deposition

Abstract

Disclosed is an improvement in a method of making a primary current detector by plasma enhanced chemical vapor deposition, where a gas mixture comprising a carrier gas, a dopant gas, and silane gas is passed through a plasma in a vacuum chamber thereby forming, on a conductive substrate, deposits of a blocking layer which comprises doped hydrogenated amorphous silicon, and then a photoconductive layer which comprises hydrogenated amorphous silicon. The improvement comprises controlling the process parameters within defined limits while reducing the flow of the silane gas to the vacuum chamber so as to deposit on the photoconductive layer a passivation layer about 0.05 to about 0.5 micrometers thick which comprises hydrogenated amorphous silicon doped with about 100 to about 2000 ppm of a dopant. Also disclosed is a primary current detector made by this method.

I claim: 
     
       1. In a method of making a primary current detector by plasma enhanced chemical vapor deposition, where a conductive substrate is placed in a vacuum chamber and a gas mixture comprising a carrier gas, a dopant gas, and silane gas is passed through a plasma thereby forming on said conductive substrate, first a blocking layer which comprises doped hydrogenated amorphous silicon, then an intrinsic photoconductive layer which comprises hydrogenated amorphous silicon, the improvement which comprises thereafter, as necessary, adjusting the total gas pressure to about 0.11 to about 0.33 kPa, the plasma power to about 25 to about 150 mwatts/cm 2 , and reducing the flow rate of said silane gas to said vacuum chamber to 0 to 5 sccm to produce a total gas flow rate of about 5 to about 150 sccm, so as to deposit on said photoconductive layer a passivation layer about 0.05 to about 0.5 micrometers thick which comprises hydrogenated amorphous silicon doped with about 100 to about 2000 ppm of a dopant. 
     
     
       2. An improvement according to claim 1 wherein said plasma enhanced chemical vapor deposition process is not interrupted in between the formation of said layers. 
     
     
       3. An improvement according to claim 1 wherein the product of the dopant concentration and the thickness of said dopant in said passivation layer is less than the charge density placed on said primary current detector. 
     
     
       4. An improvement according to claim 1 wherein said flow of said silane gas to said vacuum chamber is abruptly and completely terminated to form said passivation layer. 
     
     
       5. An improvement according to claim 1 wherein said dopant gas is diborane gas. 
     
     
       6. An improvement according to claim 5 wherein the concentration of boron in said passivation layer increases continuously from a minimum at the interface of said passivation layer with said photoconductive layer to a maximum at the opposite side of said passivation layer. 
     
     
       7. An improvement according to claim 1 wherein said blocking layer and said passivation layer are doped with p-type dopant. 
     
     
       8. An improvement according to claim 7 wherein said dopant is boron. 
     
     
       9. An improvement according to claim 1 wherein said blocking layer and said passivation layer are doped with an n-type dopant. 
     
     
       10. An improvement according to claim 9 wherein said dopant is phosphorus. 
     
     
       11. An improvement according to claim 1 wherein the concentration of said dopant in said passivation layer is about 600 to about 1400 ppm. 
     
     
       12. An improvement according to claim 1 wherein said substrate is a cylinder. 
     
     
       13. An improvement according to claim 1 wherein said substrate is aluminum. 
     
     
       14. An improvement according to claim 1 wherein said photoconductive layer is about 5 to about 75 micrometers thick and contains boron at a concentration of about 5 to about 50 ppm. 
     
     
       15. An improvement according to claim 1 wherein said blocking layer is about 0.05 to about 5 micrometers thick and is doped with boron at a concentration of about 100 to about 2000 ppm. 
     
     
       16. An improvement according to claim 1 wherein the temperature of said substrate is about 190° to about 300° C.